Photosensitive electron emission cell



May 14, 1957 R. J. HERBOLD PHDTOSENSITIVE ELECTRON EMISSION cm.

Original Filed June 21, 1952 IFIG.|

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INVENTOR ROBERT J. HERBOLD ATTORNEY United States atent g 1...,

2,792,516 PHOTOSENSITIVE ELECTRON EMISSION CELL Robert J. Herbold,Denver, Colo.

Ori al application June 21 1952 Serial No. 294,941. D iv ided and thisapplicatioii Ma 28, 1953, Serial No. 363,834

1 Claim. (Cl. 313-96) This invention relates to a photosensitiveelectron emission cell which serves in electronic apparatus forstabilizing the attitude of moving craft and instruments carriedthereby.

Various problems are involved in stabilizing a craft during its normaltravel or in stabilizing a support for apparatus mounted on a rolling orpitching boat or aircraft. The stabilization of a moving body requiresan invariable reference plane or direction of energy or other constantuni-directional medium with reference to which the position of the craftmay be compared. The direction of terrestrial electromagnetic lines offorce which afiect a compass varies for different locations on the earthand does not provide a satisfactory reference for some conditions.Gravity is uni-directional, but at the high speeds now feasible forcraft flight, the action of gravity alone is insufficient for areference. Also, gyroscopes and related instruments require complexstructural features to compensate for variable conditions, but these areaffected by the extremely high speeds that are now feasible. It isdesirable to have a horizontal or other plane which may serve as areference for various instruments.

I propose to employ an electronic device for determining or controllingan instrument or craft attitude, but this depends upon the provision ofan invariable plane for the reference. For that reference, I use theearth horizon or the horizontal plane that is perpendicular to an earthradius at the point of location ofthe craft.

The primary object of my invention is accordingly to provide avphotosensitive electron emission cell. for use in electronic apparatuswhich employs the horizon as a ref.- erence plane and which has photoemissive cathodes and anodes arranged to scan all quadrants of thehorizon, and wherein the activation of the cathodes depends upon theangularity of the light rays impinging thereon. Further objects will beapparent in the following disclosure.

The electronic apparatus in which my tube is used is described andclaimed in my copending application, Serial No. 294,941, filed June 21,1952. The operation of that electronic scanning device, which views theearth horizon and electrically responds or indicates when a horizontalplane is maintained with reference thereto, is based on the fact thatwhen an aircraft is at a sufficiently high altitude, the earth horizonprovides a substantially horizontal reference plane perpendicular to theearth axis at. that point, irrespective of mountains and other surfaceirregularities. Similarly, the horizon of the ocean appears to besubstantially in a horizontal plane when viewed from a high point. on abeat. Light from the sky may be employed to activate the photo sensitivecement of the cell herein claimed which is in a condition of saturationfor a minimum light intensity, and that cell will respond according, towhether its activation is caused by the greater light from the sky'orfrom the lesser earth light. Hence, if the cell is tilted toward thesky, it gives. a larger outputthanwhen; it:

scans the earth. The electronic system is such that it is balanced forthe variable ambient light and therefore responds only to a variation inthe ratio of the sky and earth lights as is caused by a tilting of thecraft. This differential activation which distinguishes between earthand sky light is provided by so shadowing the photosensitive elementthat any tilting of the cell vanes its area of activation and thereforethe cell output. My device is so constructed thatthe electronicactivation is proportional only to the photosensitive area illuminated.

Referring to the drawings which diagrammatically illustrate anembodiment of this invention:

Fig. l is a front view of a shielded phototube held vertically and withthe upper half of the cathode in the shadow of the shield;

Fig. 2 is a side view of the tube tilted towards the left, with all ofthe cathodes shadowed;

Fig. 3 is a similar view showing the entire surface of the cathodelighted when the tube is tilted to the right;

Fig. '4 is a vertical view of a compound phototube having a separatecathode and anode pair in each of four vertical quadrants;

Fig. 5 is a top plan view of the compound tube and showing inner andouter screens dividing the quadrants; and

Fig. 6 is a plan view of the bottom of the tube.

A photocell of the type shown in Figs. 1 to 3 is described in my Patentai -2,489,222 of November 22, 1949. it comprises a cathode having alight sensitive surface which has its area of activation varied inaccordance with the directive angularity of light passing the edge of ashield extending to a medial point on the cathode and arranged to shadowa variable portion of the cathode surface as the light angle changes.This cell may be so arranged that it will scan the horizon anddiflerentiate electronically between the sky and earth lights. Thephotosensitive electron emissive tube of Figs. 1, 2 and 3 may comprise acathode 10, whether a plate or a wire, having a coating of a suitablelight sensitive material and an anode 11 mounted Within a cylindrical,transparent glass tube 12. The upper half of the glass tube is envelopedby a shield 13 made of a suitable opaque material or a semi-translucentshield which will not pass or restrict certain wave lengths of light,and particularly the infrared. As shown in-Fig. 1, the shield is solocated that when the tube is vertical, ahorizontal ray of lightreprmentcd by the dotted line a just passing the lower circularhorizontal edge of the shield bisects the cathode 1a. This line a maytherefore represent the horizon, and any light from the darker earththat strikes the upper part of the cathode obviously has a lesseractinic value than has the light passing to the cathode through thetriangle between the horizon line a and the line b which just clears theedge of the shield and strikes the bottom edge of the cathode. That is,the bottom half of the cathode may be activated by rays of light comingfrom above the horizon but bounded by the oblique line b. it is to beunderstood that suitable shields will eliminate other extraneous lightrays. If the tube is tipped towards the left, as shown in Fig. 2, theangle between the lines a and b representing the angle at which lightmay strike the cathode becomes smaller so that when the lines a andbcoincide the cathode'is not illuminated or activated. If the tube istipped towards the right, as shown in Fig. 3, then that angle becomeslarger and in an ultimate position of tilt the cathode is fully illuminated. This applies to the various photosensitive cells, whether theyare of the voltaic, the resistance, or photo'-- conductive, or theelectron-emissive types, and each type may be used in my system withsuitable wiring modifi= cations. A, photoconductive cell may comprise aresistance wire of selenium or other metal which has its conductivityvaried by light. A photovoltaic cell may definite angular portion of thehorizon and thus is acti- 'vated in accordance with the tilt of thephotocell and the corresponding angularity of the light which passes theshield onto the cathode. In order that variations in light conditions,such as are found when the craft is within a heavycloud, may not affectthe control apparatus, I

employ a pair of balanced tubes for each sector of the horizon. Thebalanced tubes may be similar in their characteristics and arranged toreceive the same directional light, except that the shield is omittedfrom one so that it is affected by the ambient light at all times. Thesetwo tubes are so arranged in a balanced bridge circuit that anyvariation in light intensity will affect each of the tubes equally andthus counteract such variation.

The four shielded tubes are consolidated in a compound construction ,asshown in Figs. 4, 5 and 6. This comprises a glass or other translucent,substantially cylindrical tube 20 having four opaque partitions 21arranged diametrically and vertically therein and shaped to divide theinner cylindrical space into four vertical quadrants. These partitionsmay be made of metal, plastic or other material that will not transmitthe activating rays of light from one compartment 'to another. Mouned atthe rear in each wide angled quadrant is a cathode 24 having its activesurface facing outwardly, and in front is an anode 25. These aresuitably positioned and shaped to satisfy the requirements ofthe'inventiou. The cathode may be a flatplate activated on its frontexposed face, as shown in Fig. l, and the anode may be a centrallylocated metal rod or a rectangular metal frame. The cathode may be madeof a set of coated wires mounted on a rectangular frame, as described inmy copendiug application Serial No. 228,267 filed May 25, 1951. In thatconstruction, the cathode comprises a rectangular nickel or other metalwire frame carrying a set of parallel wires of nickel coated with silverand sensitized by means of a coating of caesium metal on a base ofoxidized caesium laid on the silver, which is so treated as to provide asurface that is sensitive to or activated by infrared light inparticular.

'The outside of the glass wall 20 is provided with a shield 26, like theshield 13, which is adapted to cut off the infra red rays of light thatwould activate the cathode. The shield is arranged to protect or shieldhalf of the cathode from a horizontal ray. The shield 26 may be formedby coating the outer surface of the glass with a suitable gelatin, suchas corresponds with a Wratten gelatin filter #64, 65 or 67, whichtransmits light other than red and infrared. Such a shield permitsactivation of all of the cathode surface by embient light but shadows itonly for the red and infrared rays, or other rays selected for thepurpose. Since the earth is a source of infrared rays it is desirable toshield the cathode from such Wave lengths. This screen may also be madeof a film of cellulose acetate or nitrate applied on the outside of theglass to the required thickness to shield the cathode. The translucenceof this film may be controlled by adding opaque powders or dyes, such asby incorporating a small amount of dispersed graphite or a dye in anitrocellulose solution before it is applied to the glass surface. Thisshield may also be made of an entirely opaque material to shut 013 alllight rays from the cathode areas shadowed thereby. Infrared rays travelin straight lines and there is little or no ambient infrared light inthe air which would affect the operation of the device. Instead ofcoating the glass, a capor band of suitable material may be shaped andfitted over the outside of the tube. Various other expedients may beemployed. 'In order to protect each cathode from light coming fromanother quadrant, I

4 may also provide an outside shield comprising four vertical partitions28 arranged at right angles to serve as continuations of the innerpartitions 21, and these may be suitably mounted for the purpose.

Mounted within the same quadrant'defined by each adjacent pair of outerpartitions 28 is a second balancing tube which has the same electroniccharacteristics as the one provided with the shield 26. This balancingtube may be a compound tube like that shown in Figs. 4, 5 and 6 andhaveidentical characteristics except for the absence of the shield 26. Inthat case, only two of the compound tubes are required in the system. 7

These tubes may be suitably mounted on thecraft where they may scan thehorizon and some of the sky light. For example, the fuselage of thecraft may carry a suitable downwardly projecting bay formed oftransparent material capable of passing all of the required actinicrays. The pair of balanced tubes may be suitably mounted where theyproject downwardly from an opaque Wall and in that case the shield 26will be at the bottom of the tube as shown in Fig. 4 and so will extendfrom the top base plug downwardly half way across the cathode. Thecompound tubes (Fig. 4) scan in all directions and only two are needed,one mounted vertically above the other. The base of the multiple cathodetube of Fig. 4 may be provided with a suitable number of prongs 36 thatare connected properly with the respective cathodes and anodes in eachquadrant, and these prongs will be connected into the electricalcircuits as needed. Various constructional details may be employed inthe structure and mounting of these tubes, as well as the shields andthe light confining walls.

Any unbalanced condition represented by tilting the cathodes of each twocorresponding cell quadrants facing in a given direction can be employedto actuate a control mechanism governing the position of the cathoderelative to a vertical line. For example, an electronic circuit, whichis normally balanced when the two opposed seats of cells are vertical orat a desired angle, may be employed to control a servomotor which inturn governs or actuates mechanism that controls the position of thephotocells. The four photocell quadrants of Fig. 5 are connectedelectrically in two separate circuits, having oppositely facing cells ineach circuit. That is, cells facing north and south, for example, willbe in one circuit, and the east, west cells in the other. These twocircuits are electrically alike. As one system which operates to thisend, and as described in said copending application a reversible motorwhich controls the ailerons or elevators of an aircraft may have itsfield or armature current varied in accordance with the directive angleillumination and activation of the cathodes, as indicated by theresponse of the unbalanced circuit, to cause the motor to so adjust thepositions of the ailerons or elevators as to bring the craft, or aplatform carrying various instruments, back to a normal horizontalposition.

Opposite cathodes of each cell scan the horizon in op posite directionslateral of the craft and thus control the lateral variation from ahorizontal, while the other opposite cathodes scan the horizon to thefront and rear or at right angles to the first pair to control the pitchor forward tilt of the craft.

Each cathode of the shielded cell is so shielded by walls and partitionsthat its activation is dependent of the angular tilt of the cellrelative to the horizon. That is, each cathode is so shielded that itsactivation is varied in accordance with whether the major light receivedby it is derived from the sky or is reflected earth light.

. Thus, the horizon forms a boundary line which is indirectly caused toshadow the photosensitive element to a varying extent. Consequently,that element, which may be balanced for a given horizon shadow effect,will have its electrical output varied in accordance with the cellactivation.

Various modifications will be readily apparent to one skilled in theart. Hence, the above description of preferred embodiments is to beinterpreted as defining and illustrating the principles of my inventionand not as imposing limitations on the appended claim.

This case is a division of my copending application, Serial No. 294,941,filed June 21, 1952.

I claim:

A photosensitive electron emission cell comprising a transparentsubstantially cylindrical tube arranged for receiving light throughoutthe 360 angle about the tube axis, light restricting partitions arrangedsubstantially radially of the tube axis which form separate compartmentsracing only outwardly between radial planes, a photosensitive cathode ineach compartment independent of the partitions which has its lightsensitive surface facing outwardly, a separate anode associated witheach cathode, a separate pair of terminals connected respectively withthe cathode and anode in each compartment, said partitions and cathodesbeing so shaped and arranged that the scanning field of each cathode isconfined by and between the adjacent partitions and without substantialoverlap ping of the fields of adjacent cathodes, the cathodes scanningsubstantially the entire circumference within a limited vertical anglewhen the axis of the cell is vertical, and a light restricting shieldassociated with and having an edge intermediate of each cathode arrangedto shadow the cathode vertically and provides an area of activationthereof which varies with the directive angle of light rays relative tothe edge of the shield.

References Cited in the file of this patent UNITED STATES PATENTS2,001,685 Law May 14, 1935 2,166,672 Baker July 18, 1939 2,489,222Herbold Nov. 22, 1949 FOREIGN PATENTS 906,557 France May 22, 1945

